In the wake of Monday’s Navy Yard shooting, there has been much lamentation that mass shootings are on the rise in America. “If you have been thinking that we live in an era that is more marked by this type of mass bloodshed than any era before,” remarked Rachel Maddow, “I am sad to tell you you are right. It did not used to be this way, but more and more, this is part of how we live.”

The problem with this claim is that it isn’t true – or to be more charitable, it’s “true” in such a limited way as to be meaningless.

Maddow is defining “this type of mass bloodshed” as mass shootings in which 12 or more victims were killed. There have been 12 such shootings in the United States since 1949, and half of them have taken place in the last six years, which on its face sounds, as Maddow suggests, like a very ominous trend.

But anyone familiar with statistics should be made immediately suspicious by what statisticians refer to as the “cut point” for Maddow’s analysis. Why did she choose 12 victims? The answer is because it created the appearance of a statistically significant trend, where no such trend exists.

Suppose Maddow had defined “this type” of mass shooting as one in which at least 14 victims died. Using that definition, it turns out that the rate of this type of mass shooting in America was nearly twice as high in the 25 years between 1966 and 1991 as it has been in the 22 years since (there were four such shootings in the former period, and two in the latter).

Or we could use the FBI’s definition of a mass shooting: one in which at least four people, not including the perpetrator, are killed. This is a vastly larger category than the one Maddow employs: there were about 600 such incidents in the United States between 1980 and 2010. As James Alan Fox, a professor of criminology at Northeastern University points out, the rate of such mass shootings does not appear to be rising.

Speaking of statistics, here are a few others that ought to be relevant to policy makers:

*Homicide rates in the United States are lower now than they have been at almost any time in the last century, having fallen by more than 50% since 1991.

*Mass shootings, even using the very broad definition employed by the FBI, make up a tiny fraction of homicides – usually less than one percent.

*No one knows why homicide rates doubled between 1960 and 1980, or why they’ve declined just as sharply in the years since. Many theories have been suggested, including the aging of the population, high rates of incarceration, legalized abortion, and even declines in the percentage of lead in the environment (the latter, improbable-sounding, hypothesis has some surprisingly strong statistical support). But criminology is very far from an exact science, and these various theories remain little more than educated guesses.

Given all this, it’s very difficult to say what, if anything, can be done about either gun violence in general, or mass shootings in particular. It seems unlikely that the kind of weak gun control measures that are politically conceivable in America today, such as limits on certain sorts of weapons, and tighter background checks, will make much if any difference in regard to social problems that we, at bottom, do not really understand.

That is a frustrating and somewhat depressing conclusion, especially since even today’s far lower homicide rate is still vastly higher than that in almost all other wealthy industrialized nations. But it is better to admit to not knowing what to do than to do something for the sake of pretending otherwise.

there will always be mass shootings as long as there are mentally ill people out there. weather it be the religious fanatics like muslims, or PTSD cases or disgruntled employee. The only thing that can be done is not become complacent at the work place or do not be a bully and abusive to employees. It is not cost effective for small business to complete background investigations like the Govt can. But they need to know there employees and look for signs especially after termination. The Govt and contractors need to do very complete background checks. You can not catch every mental person or some with issues out there some will slip the the cracks. Security needs to be professional not a 65 year old guard that is retired from teaching school. company.s get what they pay for and most do not give the priority to security needs. they think it will never happen to them.

Thank you for mentioning the lead-paint hypothesis, which is really the only theory I have found which truly explains the huge swings in violent crime over the last half-century.

And not only does it explain the changes over time, it also explains geographical differences as well. It is no coincidence that crime rates are still relatively high in poor urban neighborhoods where the amount of lead in the environment is significantly higher than in other places.

The biggest problem with this the lead paint theory is that powers that be don't want to hear it. They don't want to recognize the fact that, as a society, we engaged in mass poisoning on an epic scale when we permitted lead as an additive to gasoline. And they really don't want to recognize the fact that environmental policy, not "more modern and effective police techniques" are the reason that crime has declined. Much better to our militarized and corporatized police departments take credit than acknowledge that our ever-expanding police state has little to do with it.

Thank you for this. After the shooting, I had trouble with a lot of data I was seeing suggesting mass shootings were on the rise. Was it just an anomaly? Or was something bigger at play? What was going on? Turns out, as usual, statistics seem to have been manipulated to demonstrate a trend that wasn't there.

@Openminded1 You bring up some good points, but while you can't reach everyone who has sort of dangerous mental condition, I think lessening the stigma associated with seeking mental help could definitely help. Also, as medicine advances we'll be increasingly able to help those who can't help themselves. Looks like better news for the future!